ABSTRACT
We present the results of our investigation of metallic films as suitable materials for the production of intense electron beams. Thin films of Y prepared for the first time by pulsed laser deposition on Si substrates have been tested as photocathodes in an ultra high vacuum photodiode chamber at 10(-6) Pa. High quantum efficiencies have been obtained for the deposited films, comparable to those of corresponding bulks. The role of the adsorbed gases on the emission performance has been studied. Systematic laser cleaning treatments improved the quantum efficiency (QE) from 10(-6) to 4.5 10(-4). The samples could stay for several months in open air before being tested in a photodiode cell. The deposition process and testing results are presented.
ABSTRACT
In this Letter we report the first experimental observation of the double emittance minimum effect in the beam dynamics of high-brightness electron beam generation by photoinjectors; this effect, as predicted by the theory, is crucial in achieving minimum emittance in photoinjectors aiming at producing electron beams for short wavelength single-pass free electron lasers. The experiment described in this Letter was performed at the SPARC photoinjector site, during the first stage of commissioning of the SPARC project. The experiment was made possible by a newly conceived device, called an emittance meter, which allows a detailed and unprecedented study of the emittance compensation process as the beam propagates along the beam pipe.
ABSTRACT
We present the first observation of self-amplified spontaneous emission (SASE) in a free-electron laser (FEL) in the vacuum ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approximately 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width, and intensity fluctuations, are all consistent with the present models for SASE FELs.